In manufacturing a semiconductor element formed from a micropattern, such as an LSI or a VLSI, a reduction projection exposure apparatus is used to form, by exposure, a circuit pattern drawn on a reticle or a mask by reducing and projecting it onto a wafer coated with a photosensitive agent. Along with an increase in mounting density of a semiconductor element, further micropatterning is required. The exposure apparatus takes a measure to implement micropatterning at the same time as the development of a resist process.
Unfortunately, if a particle such as dust adheres to the substrate surface in pattern transfer, the particle is also transferred in the circuit pattern, resulting in a large decrease in manufacturing yield of an IC or LSI. For this reason, a mask or reticle generally has a pattern protective member, called a pellicle, consisting of transparent thin films, which are made of cellulose nitrate and have a thickness of about 1 μm. This prevents a particle such as dust from adhering to the reticle pattern surface.
If a particle adheres to the reticle blank surface or a pellicle surface spaced apart from the reticle pattern surface, the particle is not transferred onto a wafer. However, a defocused image of the particle adhering to the above-mentioned surface may possibly be transferred, so the light amount varies on the wafer, resulting in unsatisfactory exposure.
To solve this problem, the presence/absence of a particle on a reticle (blank surface) or a pellicle must inevitably be detected before and/or after exposure in manufacturing an IC or LSI. A general method takes advantage of a nature in which a particle diffuses light isotropically. For example, parallel light beams are collectively applied to the inspection surface region obliquely from above. Scattered light from a particle is applied onto a one-dimensional image sensor (sensor array) by a microlens array of a refractive index distribution type to image the particle. Then, the inspection surface is inspected to detect the presence/absence of a particle (to be referred to as a foreign particle or contaminant hereinafter).
FIG. 12 is a view showing an outline of the structure of a particle inspection apparatus. A reticle 1 and pellicle 2 (not shown) as inspection objects are held on an inspection table 6. An inspection light forming unit (also to be referred to as an irradiator) 7 forms inspection light and irradiates an inspection object with it. A reticle side detector 3 faces the reticle 1 and detects inspection light applied to the reticle 1. A pellicle side detector 4 faces the pellicle 2 and detects inspection light applied to the pellicle 2.
The inspection light forming unit 7 scans the reticle side detector 3 and pellicle-side detector 4 in the direction of an arrow (x direction) with respect to an inspection object to inspect the entire surface of the inspection object for a particle.
FIG. 13 is a side view of FIG. 12 when viewed from the x direction, and a structure on the pellicle 2 side is omitted.
Referring to FIG. 13, the inspection light forming unit 7 collectively applies inspection light beams 14a as parallel light beams to the reticle 1. The applied inspection light beams are detected by the detector 3 to detect a particle.
At this time, part of the inspection light beams 14a emitted from the inspection light forming unit 7 comes from an edge portion 1a (end face portion) of the reticle 1 and enters the reticle 1. The entered inspection light is sometimes diffracted by a pattern 20 drawn on the reticle 1 to generate a diffraction light beam 21. When the diffraction light beam 21 strikes the detector 3, it is erroneously detected as scattered light from a particle. This disables accurate particle detection.
As disclosed in Japanese Patent Laid Open No. 58-79240, a shield member is conventionally arranged in a direction in which scattered light from a particle is not shielded while shielding stray light such as diffraction light in a detector. However, a direction in which diffraction light is generated depends on the pattern of a reticle, so it is difficult to shield diffraction light in every state.